1. Technical Field
This invention relates to a bumper bar for vehicles and a method for manufacturing the same.
2. Description of the Background Art
There are many demands on, and desires for, a completed vehicle. These include that the vehicle should protect passengers and load in a collision. This is achieved in that various components in and on the vehicle are designed and constructed to absorb energy, to distribute energy and to conduct energy during a collision.
If the transfer of energy from a collision object to the vehicle is limited, for example if the vehicle drives into a collision object at low speed, the parts should mainly absorb and distribute the forces so that as small a change of shape as possible takes place in the vehicle and its components. It is preferable that the change of shape is temporary, so-called xe2x80x9celastic deformationxe2x80x9d.
If the transfer of energy from the collision object to the vehicle is large, for example if the vehicle drives into a collision object at high speed, the components that absorb energy should absorb and distribute the forces in such a manner that the energy is used in a controlled way as far as is possible, for example, by using the energy to destroy certain components of the vehicle that have been specified in advance and constructed for this purpose, and that can be easily replaced after the collision. This is usually called xe2x80x9cplastic deformationxe2x80x9d.
A number of different construction components are usually required to handle the energy and to provide all of the functions that are required during different collisions. The components and the zones that absorb energy thus often become large, clumsy and expensive with respect to the constituent material, handling during manufacture and in the completed vehicle.
Furthermore, the vehicle must have a design that provides the required driving properties, external and internal dimensions and spaces. The vehicle must also have an appearance that corresponds to the wishes and expectations of the customers. There are often conflicts between traffic safety and the design of a vehicle. Vehicles that are small, fast and often minimalist in form attract more purchasers than larger vehicles with several and well dimensioned safety zones do.
There are also a number of demands and wishes that must be satisfied during manufacture of the vehicle. These can be associated with environmental, manufacturing technical and, not least, economic aspects before, during and after the actual manufacture.
The increased demands for traffic safety have resulted in an altered basic construction of bumper bars. It is nowadays normal for the bar to have a closed cross-section. This design of the bar results in the bumper absorbing collision forces and torsional loadings, and distributing extensions in an optimal manner. The closed cross-section, however, makes the bar large and means that it requires a lot of space, and it is often difficult to mount in the space available in a vehicle body.
EP 0 449 599, A1, shows a roll-formed bumper and a method for making the same. The bumper has a closed cross-section. The bumper has been pressed and deformed at the ends to a construction that is essentially flat, in order to facilitate the mounting of the bar. The deformation results in a reduction in the outer dimensions of the bumper in one direction, and an increase in another direction, see FIGS. 13-15. This is, naturally, a disadvantage if the space available is limited in more than one direction. The deformation gives rise to tensions in the material that are difficult to control, not least during a collision.
U.S. Pat. No. 005603541, shows a bumper bar with an open cross-section, which is constructed such that its shape can be changed. The ends of the bar are provided with parts that can be bent inwards. When these parts are bent or folded into the bar construction, in the direction of the front of the vehicle, the ends of the bar can be shaped and given the desired appearance. Many operations and manufacturing stations are required to obtain a bar that is ready to mount, and this is expensive. The collision properties of the bar are also affected since it is a question of the removal of material and various processing operations of the material itself, which give rise to tensions and alterations of the material.
Known constructions of bumper bars do not offer any complete solutions to the demands and desires that exist. It is an intention of the present invention to offer a bar that makes it possible to manufacture vehicles that are safe in traffic within the strict technical and economic tolerances that exist in the vehicle industry. The invention also makes it possible to make the manufacture of vehicles that are safe in traffic more cost-effective. An embodiment of the invention will here be described with reference to the figures. Further advantages and features of the invention will be described.